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Biomedical subjects

N B Alexander

Publications and source records attributed to N B Alexander.

16 recordsLinked to original sources
PubMed1995

Association of age with the threshold for detecting ankle inversion and eversion in upright stance.

A randomized quadruple staircase method and probit analysis were used to measure the thresholds for sensation of ankle inversion and eversion by 18 healthy young and 18 healthy old subjects while standing with a foot in a servo-driven cradle. The results of over 3600 trials show that the mean threshold for detecting inversion with a probability of 75% was 0.35 degrees in the older subjects, a value significantly greater than the 0.06 degrees threshold found in the younger group. The corresponding thresholds in eversion were significantly greater in both old (0.52 degrees) and young (0.35 degrees) subjects. Significant, but smaller, age differences were also found in unipedal stance. Few significant sex differences were found. When the velocity of a 0.1 degree inversion movement was increased from 2 to 200 degrees/s the probability of detecting it rose by only 22.6%. Although significantly increased with age, the threshold for sensing rotation in the weight-bearing ankle was measured in tenths of degrees, an order of magnitude better than previously reported (non-weight-bearing) values.

Adult↗
PubMed1995

Neuropsychological predictors of complex obstacle avoidance in healthy older adults.

Global cognitive impairment in older adults has been associated with a greater risk of falling, and tripping has been implicated as an important factor in a large percentage of these falls. In order to evaluate the role of specific cognitive domains in tripping and falling, 23 healthy older adults completed basic and complex obstacle avoidance tasks, as well as a battery of neuropsychological tests. Using multiple regression analysis, a select pattern of neuropsychological measures was found to predict the decrement in performance evident as avoidance task complexity increased. Whereas measures of problem solving, response inhibition, general anxiety, and variability in attention were found to be significant predictors (in that order) of the relative decline in successful obstacle avoidance, measures of visuo-spatial discrimination and memory did not.

Accidental Falls↗
PubMed1995

Healthy young and old women differ in their trunk elevation and hip pivot motions when rising from supine to sitting.

OBJECTIVE: To describe the differences between healthy young and older women in regards to trunk elevation and hip pivot motions when rising from a supine to a seated position. DESIGN: Cross-sectional comparison. SETTING: University laboratory. PARTICIPANTS: Two groups of healthy female volunteers: young adult female controls (n = 22, mean age 23.5 years) and community-dwelling older female adults (n = 17, mean age 73.8 years). MEASUREMENTS: Subjects were videotaped as they performed three controlled bed mobility tasks, starting from a supine position: (1) rising to a seated position at the edge of a firm plinth surface (SS); and rising to a seated position without moving to the edge of the bed while either (2) using hands (SUH) or (3) not using hands (SUNH). A series of movements involving the trunk were identified as subjects performed the SS task. RESULTS: The older women were more likely to rotate and laterally flex their trunks, particularly in the later phases of the SS task. In addition, during the SS task, the older group was more likely to bear weight on their hip/gluteal area, particularly in the later phases, and more likely to use a broad pivot base, consisting of the hip and the elbow. While all young and old performed the SUH task, less than half of the older group could complete the SUNH task. Moreover, the subgroup of older adults who could not complete the SUNH task may have accounted for much of the differences between the young and the old on the SS task. CONCLUSION: Healthy young and older women differ in their ability to rise from a supine to sitting position, primarily in the strategies used to elevate the trunk and facilitate a pivot. Trunk flexion ability likely contributes to the age group differences noted in rising. These data provide the basis for a biomechanical analysis of the critical body segment motions and the strengths required to perform bed mobility tasks.

Adult↗
PubMed1995

Maintenance of balance, gait patterns, and obstacle clearance in Alzheimer's disease.

Patients with cognitive impairment, particularly as a result of Alzheimer's disease (AD), are at increased risk for falls, but it is unclear how, or if, they differ from normal adults in their balance, gait, or ability to clear an obstacle in their path. Using an optoelectronic camera system, we compared body motions and force output at the feet in patients with probable AD (n = 17) with those in healthy older adults (n = 15) while they stood on a force plate or on a beam attached to the force plate that was either stationary or accelerating. Using the same camera system and comparing this AD group with another group of healthy older adults (n = 24), we observed the AD patients during normal walking and while clearing 25- and 152-mm-high obstacles. None of the AD patients had extrapyramidal signs or musculoskeletal impairments. Compared with healthy older adults, normal walking speed was significantly slower in the AD group (p < 0.0001). While clearing either obstacle, the AD patients were significantly slower in their approach (p < 0.0001) and crossing (p < 0.0001) speeds and landed closer to the obstacle after having crossed it (p < 0.02). Moreover, the percent of trials in which a subject made contact with an obstacle was significantly higher in patients with AD (p < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Effects of age and available response time on ability to step over an obstacle.

BACKGROUND: Falls during walking are often triggered when a foot contacts an obstacle in its path. Yet little is known about the ability of individuals of any age to successfully negotiate obstacles, especially under time-critical conditions. METHODS: The gait of 24 young and 24 old healthy adults (mean ages 23 and 73 years) was studied as they approached and tried to avoid stepping on a band of light, not knowing when or where it might appear on an 8 m-long walkway. This virtual obstacle was placed at the predicted location of the next footfall with available response times (ART) before heel strike that were varied randomly in 50 ms increments from 200 to 450 ms. In addition, their gait was observed as they stepped over a fixed virtual obstacle and over an obstacle that appeared with approximately a 1000 ms ART. RESULTS: The old had an increased risk of obstacle contact while negotiating obstacles under time-critical conditions (p = .082). Mean rates-of-success (RS) in obstacle avoidance for the young ranged from .205 at a 200 ms ART to .969 at a .450 ms ART. Corresponding mean RS for the old were .157 and .920. Lower extremity simple reaction time (SRT) test made under static conditions showed that the mean SRT of the old were approximately 80 ms longer than those of the young. Regression analyses suggested that the old in fact would have needed only 30 ms additional ART to achieve RS equal to that of the young for obstacles appearing with ART from 300 to 450 ms. CONCLUSIONS: Reductions in ART significantly decreased RS. Delays as small as 50 or 100 ms in observing or reacting to obstacles in real-life situations may significantly lower the rate of success that subjects of any age have in avoiding them. Age differences in SRT do not always reliably indicate age differences in obstacle avoidance under time-critical situations.

Accidental Falls↗
PubMed1994

Stepping responses of young and old adults to postural disturbances: kinematics.

OBJECTIVES: When large disturbances of upright stance occur, balance must usually be restored by taking a step. We undertook this study to examine the biomechanics of stepping responses to sudden backward pulls at the waist. Primarily, response differences between young and old healthy adults were sought. DESIGN: A controlled laboratory study. SUBJECTS: Two groups of healthy and physically-fit adult females, 12 of mean age 22 (Young) and 12 of mean age 73 years (Old). MEASUREMENTS: Response kinematics were measured. From them, the stepping strategies of the subjects were derived, including the timing, length, and height of the first step taken and the rotations of major body segments and at major body joints that occurred. RESULTS: In response to sufficiently large backward pull forces, all subjects responded by taking one or more steps backwards. No significant age group difference appeared in the smallest disturbance for which subjects sometimes used a step response. A significant age group difference appeared in the smallest disturbance at which subjects began consistently to use step responses, and that disturbance was larger for the Old than for the Young. Distinct age group differences were found in stepping strategy. At large disturbance levels, the Young mostly responded by taking a single step, whereas the Old mostly responded by taking multiple steps. The steps taken by the Old, compared with those of the Young, were significantly shorter, had significantly smaller heights, and were taken significantly earlier in the responses. Body segment and joint rotations were generally modest, and few significant age group differences were found in these kinematics. CONCLUSIONS: In restoration of perturbed balance by step-taking, the responses of the healthy, physically-fit young and old adults studied here were similar in many respects, but they differed in some important features. Joint range of motion (ROM) limitations are unlikely to explain age group differences in stepping responses to postural disturbances among healthy subjects because the ROM actually used in any of the responses observed were substantially smaller than the ROM available.

Adult↗
PubMed1993

Postural control in young and elderly adults when stance is challenged: clinical versus laboratory measurements.

The use of dynamic posturography (EquiTest) for the characterization of postural control biomechanics would be aided by specific knowledge of what the measured data imply about body segment movements. To investigate this issue, the biomechanics of a group of 15 healthy elderly subjects were compared to those of healthy young subjects by using both dynamic posturography and a laboratory movement and force measuring system. The results from EquiTest were analyzed by 1) routine clinical interpretation of data and 2) a clinical research interpretation by subjecting the EquiTest parameters to additional statistical comparison of mean performance of the young and elderly groups. The young-elderly differences from the 2 EquiTest analyses were then compared to the young-elderly differences derived from the laboratory protocol. The routine clinical interpretation of EquiTest data identified the same increases in sway shown by the laboratory study, but did not reveal the more subtle differences indicated by the laboratory study. When the EquiTest data were subjected to additional statistical analysis, the characterization of difference between young and elderly subjects was the same as that of the laboratory study, with the exception of issues of head versus trunk movement, a measure not made by EquiTest. This essential similarity in the characterization of elderly compared to young subjects by both systems suggests 1) that EquiTest is able to detect subtle differences in biomechanics of postural control between young and elderly healthy adult groups and 2) that implied movements of center of gravity, trunk versus lower limbs, and strength of reaction measures are consistently detected by both EquiTest and the laboratory kinematics and dynamics measurement systems.

Adolescent↗
PubMed1992

Biomechanical analyses of rising from a chair.

Quantification of the biomechanical factors that underlie the inability to rise from a chair can help explain why this disability occurs and can aid in the design of chairs and of therapeutic intervention programs. Experimental data collected earlier from 17 young adult and two groups of elderly subjects, 23 healthy and 11 impaired, rising from a standard chair under controlled conditions were analyzed using a planar biomechanical model. The joint torque strength requirements and the location of the floor reaction force at liftoff from the seat in the different groups and under several conditions were calculated. Analyses were also made of how body configurations and the use of hand force affect these joint torques and reaction locations. In all three groups, the required torques at liftoff were modest compared to literature data on voluntary strengths. Among the three groups rising with the use of hands, at the time of liftoff from the seat, the impaired old subjects, on an average, placed the reaction force the most anterior, the healthy old subjects placed it intermediately and the young subjects placed it the least anterior, within the foot support area. Moreover, the results suggest that, at liftoff, all subjects placed more importance on locating the floor reaction force to achieve acceptable postural stability than on diminishing the magnitudes of the needed joint muscle strengths.

Adult↗
PubMed1992

Postural control in young and elderly adults when stance is perturbed: kinematics.

Increased postural sway and falling are associated with aging and are likely related to problems with postural control in the elderly. We investigated the motions of individual body segments in 24 healthy young adults and 15 healthy elderly adults (mean ages 26 and 72) in response to four tasks: (a) standing with feet flat on an anteriorly accelerating platform (Flat Translation); standing on a narrow beam support that was (b) stationary (Beam Standing) and (c) accelerating anteriorly (Beam Translation); and (d) standing on a rotatable but otherwise stationary springboard (Springboard Standing). An optoelectronic camera system was used to measure rotations of body segments, particularly regarding their maximum excursions, time to first rotation response, direction of initial rotation, and time to first rotation reversal. In general, larger rotation excursions were noted in the elderly compared to the young group, particularly in the Beam Standing and Beam Translation tasks, but the magnitude of rotation difference was small. All rotation magnitudes were well within the available ranges of motion of the body joints. In both excursion magnitudes and directions of initial rotation, the elderly showed greater variability than the young. In the Beam Translation task, the elderly group, compared to the young, tended to rotate their upper body segments more than in the Flat Translation task. These data suggest that healthy elderly adults with no apparent musculoskeletal or neurological impairments have small but consistent differences in postural control kinematics, particularly when more challenging conditions are presented. Moreover, these data provide the basis for biomechanical analyses of joint torques and other dynamic requirements of these responses.

Adult↗
PubMed1992

Quantitative assessment of bed rise difficulty in young and elderly women.

OBJECTIVE: To describe the motions which occur during rising from bed, specifically the motions that appeared to characterize difficulty in rising from a bed in older adults. DESIGN: Development of a Mobility assessment tool. SETTING: Retirement center and two university laboratories. PARTICIPANTS: Three groups of female volunteers: young controls (n = 17, mean age 24), community-dwelling older adults (n = 12, mean age 71), and retirement center-dwelling older adults who admitted to difficulty in rising from a bed (n = 15, mean age 86). INTERVENTION: Videotaping of motions occurring during controlled rises from a supine to sitting position. MAIN OUTCOME MEASURES: These motions were rated on the specially developed Bed Rise Difficulty (BRD) scale, a scale designed to measure movements that characterize difficulty in rising from a bed in older adults. Subject groups were compared in total BRD score, individual BRD item score, and total time to rise. Item relationships and scale reliability were also assessed. RESULTS: Older adults with no apparent difficulty in rising based on total time to rise or on the BRD score nevertheless showed differences in upper extremity use when compared to young controls. Older adult subjects with difficulty in rising from a bed, when compared to other older adults with no apparent difficulty, differed more often in their upper extremity and leg use to facilitate the rise. Five BRD scale items, including use of extremity pushes, discontinuity of trunk and leg motion, multiple shoulder/pelvic adjustments, multiple leg adjustments, and poor vertical heel clearance may have best indicated true bed rise difficulty. CONCLUSIONS: These data provide a reliable and valid method to characterize difficulty in rising from a bed and provide the basis for biomechanical analyses of the strength and joint ranges of motion required to rise from a bed.

Activities of Daily Living↗
PubMed1991

Rising from a chair: effects of age and functional ability on performance biomechanics.

Although difficulty in rising from a chair is common to elderly people, few studies have compared chair rise performance in young and elderly adults with differing functional abilities. Using an instrumented chair and a videotape analysis, controlled chair rise performances were quantified in three groups of volunteers: young adults (Young, n = 17, mean age 23 years), elderly adults able to rise without the use of armrests (Old Able, n = 23, mean age 72 years), and elderly adults unable to rise without the use of armrests (Old Unable, n = 11, mean age 84 years). Rises both with and without the use of hands were observed. The total time to rise and the percent of that time spent in the two distinct phases of the rise, the body segment rotations used, and the hand forces exerted were measured. Despite no apparent functional impairment, the Old Able compared to the Young spent a larger percent time in the first phase of the rise and rotated their body segments by different amounts. When rising with use of hands, the Old Unable compared to the Old Able group took more time and used different body segment rotations and larger ratios of hand force to body weight. These data quantify chair rise performance in young adults and in elderly adults with differing functional abilities and enable biomechanical analyses of the importance of joint torque strengths and postural stability in that performance.

Adult↗
PubMed1991

Stepping over obstacles: gait patterns of healthy young and old adults.

Falls associated with tripping over an obstacle can be devastating to elderly individuals, yet little is known about the strategies used for stepping over obstacles by either old or young adults. The gait of gender-matched groups of 24 young and 24 old healthy adults (mean ages 22 and 71 years) was studied during a 4 m approach to and while stepping over obstacles of 0, 25, 51, or 152 mm height and in level obstacle-free walking. Optoelectronic cameras and recorders were used to record approach and obstacle crossing speeds as well as bilateral lower extremity kinematic parameters that described foot placement and movement trajectories relative to the obstacle. The results showed that age had no effect on minimum swing foot clearance (FC) over an obstacle. For the 25 mm obstacle, mean FC was 64 mm, or approximately three times that used in level gait; FC increased nonlinearly with obstacle height for all subjects. Although no age differences were found in obstacle-free gait, old adults exhibited a significantly more conservative strategy when crossing obstacles, with slower crossing speed, shorter step length, and shorter obstacle-heel strike distance. In addition, the old adults crossed the obstacle so that it was 10% further forward in their obstacle-crossing step. Although all subjects successfully avoided the riskiest form of obstacle contact, tripping, 4/24 healthy old adults stepped on an obstacle, demonstrating an increased risk for obstacle contact with age.

Adult↗